For years, the nonwoven industry has attempted to produce a carded nonwoven fabric that has good cross direction strength. Generally, the fibers in carded webs are aligned in a direction substantially parallel to the direction of the web within the carding machine normally used to make nonwoven fabrics. Consequently, the machine direction strength of a carded web generally is a high multiple of the cross direction strength. A further complication is that the conventional processing of bonded nonwoven fabrics consists of a set of stages--conveying, saturating, drying, winding, etc--all of which impose a further drafting and parallelizing effect on the fibrous web. In this "normal" multi-stage bonding operation, tensile strength ratios will be found which are 10 to 20 to 1, machine direction to cross direction strengths.
Attempts to bring the so-called MD/CD ratio closer to 1 have included the use of a cross-laying device, whereby a full-width web of oriented fibers is mechanically pleated back and forth across a conveyor belt to build up a composite batt in which the average angular displacement of the fibers is alternated. Such devices are slow, cumbersome and are suitable only for batts of substantial thickness where fold marks and overlap ridges are not objectionable.
Another expedient used in the prior art to achieve better tensile strength ratios is to disperse the fibers in more or less random orientation into an air stream, from which they are collected on a conveyer screen with the aid of suction. Such devices, however, are expensive, and while satisfactory at speeds of around 10 yards per minute, they produce webs of poorer quality at speeds of over 15 yards per minute, due to clumping and poor dispersion of fibers.
It is with improvements in the art of producing fibrous webs and nonwoven fibrics of more nearly equalized machine (longitudinal) direction and cross (lateral) direction tensile strengths, as well as producing aesthetically pleasing and different nonwoven fabrics, that this invention is concerned.
Accordingly, it is an object of the present invention to produce a nonwoven fabric, initially made from a carding machine, that has an MD/CD strength ratio that approaches unity.
It is another object of this invention to produce an aesthetically different and pleasing nonwoven fabric that has this advantageous strength characteristic.
Still another object of this invention is to provide apparatus and a method of making a carded nonwoven fabric that has an MD/CD ratio that approaches unity.